Light-sensitive derivatives of vat dyestuffs and a process of preparing them



Patented Mar. 15, 1938 LIGHT-SENSITIVE DERIVATIVES OF VAT DYESTUFFS ANDA PROCESS OF PREPAR- ING THEM Paul Ochwat, Frankfort-on-the-Main-Hochst,

and Bruno Wendt, Dessau, Germany, assignors to Agfa 'Ansco Corporation,Binghamton, N. Y., a corporation of New York No Drawing. ApplicationNovember 24, 1936, Serial No. 112,610. In Germany January 11, 1932 8Claims. (Cl. 260 14.)

The present invention relates to light-sensitive derivatives of vatdyestufis and a process of preparing them.

This application is an improvement of U. S. Patent No. 2,082,178 issuedJune 1, 1937 (application Serial No. 650,590, filed January 6, 1933 inthe names of Paul Ochwat and Bruno Wendt).

We have found that light-sensitive substances of valuable properties areobtainable by reacting a water-soluble salt of a leuco ester of a vatdyestuff, the ester being formed by means of a' polybasic inorganic acidupon a watersoluble salt of an N-nitrosoaryl-hydroxylamine, aryl beingof the benzene series, inthe presence of an inert solvent. When using anester salt of a leuco vat dyestufi with a volatile base, the base may beremoved, if desired, by distillation from the reaction mixture. Theconstitution of the new light-sensitive substances is not known. Theyare applicable with advantage for photographic purposes, for instance,for the production of multi-color pictures- The leuco esters of vatdyestuffs used as parent materials, being formed by means of sulfuricacid, may be prepared according to the processes described in U. S.patent specification No. 1,448,251, British patent specifications Nos.247,787, 251,491, 260,638, or being formed by means of phosphoric acid,may beprepared according to the processes described in British patentspecifications Nos. 260,647 and'248,802.

Light-sensitive layers may be prepared, for instance, in one of thefollowing ways: The new products above mentioned may be incorporatedwith a suitable binding agent such as gelatine, glue, collodion or thelike, and this mixture may be applied on a support; or the said newproducts may be produced by combining the estersalts of the leuco vatdyestuffs and the salts of ;N-nitroso-aryl-hydroxylamines in a layer ofa binding agent which has already been applied on a support; or theproducts are incorporated with or produced, without formation of alayer, in paper, cellulosehydrate sheets or the like.

The reaction between an ester salt of a leuco vat dyestuff with abase,'such as pyridine, on the one hand, and with a salt of'N-nitroso-arylhydroxylamine, on the other hand, may be performed,: forinstance, "by' f removing with. steam the volatile ebase, from theaqueous ,solution or suspension of the components. By evaporation,

the new products are obtainable in the form of powders easily soluble inwater.

It has already been proposed to produce lightsensitive layers by meansof alkali salts of sulfuric acid esters of leuco vat dyestuffs. Thelayers obtainable according to the present invention have over the saidknown layers the advantage of yielding a better gradation and purerlights and of being more stable in the dark.

According to our new process cellulosehydrate films or sheets may beused with special advantage for the production of one-color ormulticolor pictures. As illustrated in the following examples, thesheets are impregnated at ordinary or raised temperature with therespective solution. By applying an elevated temperature, theimpregnation is accelerated, which is also the case by adding aprecipitant, such as sodium sulfate, in a quantity insufiicient forprecipitation. The addition of gylcerine to the impregnating liquorrenders the dry sheets pliable and increases, by its humidifyingaction,,the sensitiveness of the light-sensitive compound. This latteradvantage may also be achieved by the addition of another hygroscopicsubstance. In the photography of natural colors there are used separatesheets containing incorporated therewith according to one of the abovementioned methods the derivatives of the leuco compounds of a yellow, apurple-red and a bluish-green, respectively, dyestuff, which sheetsafter being printed, fixed and, advantageously, impregnated with aglycerine solution are glued together one on the other in known manner,for instance, by means of gelatine solution in paper.

Cellulose-derivative films or sheets which superficially have beenrendered sensitive to water by means of a saponifying agent, forinstance, an acetyl or a nitro-acetate film, may be used in an analogous-,manner. When used for the multi-color photography or for theproduction of ana-glyphic pictures'the two or more partial pictures, thetwo stereo pictures respectively, are printed in succession one abovethe other on a material sensitized in accordance with the invention insuch a manner that after the first printing operation the print is fixedby washing with water and the material is sensitized for the nextprinting operation and so on.

The following examples serve to illustrate the invention, but they arenot intended to limit it thereto, the parts being by weight:

(1) Into a solution containing mol. of the sodium salt of the sulfuricacid ester of leuco-4.4- dichloro-5.5-dibromindigo there is introducedpyridine hydrochloride until the dyestufi has been precipitated asdiflicultly soluble pyridine salt. The latter is isolated, made into apaste with water, mol. of the sodium salt ofN-nitrosophenyl-hydroxylamine as Well as a 10% excess thereof are added,and steam is passed through the whole until pyridine no longer distilsover.

There is obtained a solution from which the new product may be obtainedby evaporation. It forms a powder which is easily soluble in water. Whenthe solution is heated with dilute acids, the vat dyestuif precipitates.In materials impregnated with said solution the vat dyestuif is reformedon exposure to light.

In the same manner the sulfuric acid esters of other leuco vat dyestuffsmay be used for the preparation of new products. Instead ofN-nitroso-phenyl-hydroxylamine there may also be used the derivativesand substitution products thereof.

(2) In similar manner a light-sensitive product may be prepared from: 4grams of the sodium salt of the sulfuric acid ester of leuco4.4-dich1oro-5.5'-dibromindigo, 4 grams of the ammonium salt ofN-nitroso-phenyl-hydroxylamine, 20 cc. of glycerine and cc. of water.

(3) 4 grams of the sodium salt of phosphoric acid ester of leuco4.4-dimethyl6.6 dichlorothioindigo are dissolved in a mixture of 40 cc.of glycerine and 60 cc. of water and there is added to the solution 1gram of the sodium salt of N-nitroso-para-chlorphenyl-hydroxylamine.With this solution cellulosehydrate sheets are impregnated for 10minutes at room temperature and then dried. After printing, whereby apurple-red picture with pure lights is obtained, the sheets are washedwith warm water, whereby the unexposed substance is removed.

(4) A cellulosehydrate sheet is impregnated with a solution preparedfrom 5 kilos of the sodium salt of the sulfuric acid ester of leuco 4.4-dimethyl-5.7.6-trichlorthioindigo, 2 kilos of the sodium salt ofN-nitroso-phenyl-hydroxylamine, 40 liters of glycerine and liters ofwater. After squeezing off the adherent solution, the sheet is dried,rolled up and cut to the desired sizes. By printing a negative on one ofthe sheets a bluishred picture of very good gradation and pure lights isobtained, it is washed for 5 minutes in water of 70 and thereby fixed.

(5) parts of the dyestuff having the following constitution:

obtainable according to the process of Example 1 of German Patentv No.260,905, are transformed into the leuco sulfuric ester in a manner knownto be available for a like transformation in other cases. The pyridinesalt of the ester, obtainable according to the process of Example 1 ismixed while stirring, with a solution of 80 parts of the sodium salt ofN-nitroso-phenyl-hydroxylamine in water, the pyridine is distilled offwith steam, the solution is clarified and concentrated under reducedpressure. The new compound crystallizes on cooling and is filtered off.It is readily soluble in water. By heating its solution with addition ofa dilute acid the vat dyestuif is reformed.

(6) A light-sensitive product according to Example 5 is also obtained bymixing the ester of Example 5 not in the form of the pyridine saltsparingly soluble in water, but in the form of the soluble sodium saltwith the indicated quantity of the nitroso compound in the presence ofglycerine and water, as described in Example 2.

We claim:

1. The process which comprises mixing a watersoluble salt of a leucoester of the vat dyestuff of the formula:

the ester being formed by means of an acid of the group consisting ofsulfuric and phosphoric acid, with a watersoluble salt of anN-nitrosoaryl-hydroxylamine, aryl being of the benzene series, in thepresence of an inert solvent.

2. The process which comprises mixing a watersoluble salt of a leucoester of a vat dyestuif of the formula:

leuco compound of the dyestuff of the formula:

l l LY with the sodium salt of N-nitroso-phenyl-hydroxylamine in thepresence of Water and distilling off the pyridine from the reactionmixture by steam distillation.

4. The process which comprises mixing the sodium salt of the sulfuricacid ester of the leuco compound of the dyestufi of. the formula:

with the sodium salt of N-nitroso-phenyl-hydroxylamine in the presenceof glycerol and Water.

5. The compounds identical with those which are obtainable by theprocess which comprises mixing a watersoluble salt of a leuco ester ofthe vat dyestuff of the formula:

the ester being formed by means of an acid of the group consisting ofsulfuric and phosphoric acid, with a watersoluble salt of anN-nitrosoaryl-hydroxylamine, aryl being of. the benzene series, in thepresence of an inert solvent.

6. The compounds identical with those which.

are obtainable by the process which comprises mixing a watersoluble saltof a leuco ester of the vat dyestuff of the formula:

the ester being formed by means of an acid of the group consisting ofsulfuric and phosphoric acid, with a Watersoluble salt of anN-nitrosophenyl-hydroxylamine in the presence of an inert solvent.

'7. The compoundsidentical with those which are obtainable by theprocess which comprises mixing the pyridine salt of the sulfuricacidester of the leuco compound of the dyestufi of the formula with thesodium salt of N-nitroso-phenyl-hydroxylamine in the presence ofglycerol and water. V

7 PAUL OCHWAT. BRUNO WENDT.

